In order to protect the environment and promote public health, communities require wastewater treatment. The discharge of untreated wastewater is not an option, since it gives rise to numerous environmental concerns. Untreated wastewater contains bacteria that consume high quantities of dissolved oxygen, which is commonly measured as the level of biochemical oxygen demand (BOD) in the water. Thus, when untreated wastewater is released into either aboveground or belowground streams and aquifers, the level of dissolved oxygen in the water of the streams and aquifers begins to deplete, which endangers the water bodies themselves and the resident plant and aquatic life. Over time, the bacteria of the untreated wastewater will deplete the dissolved oxygen in the water to a level that will not support plant and aquatic life.
To treat wastewater, communities in highly populated areas commonly collect wastewater and transport it through a series of underground pipes to a centralized wastewater treatment plant. However, there are several problems associated with centralized treatment plants. Centralized wastewater treatment plants are designed and rated for processing a specific flow rate of wastewater per day, typically expressed as the rated capacity of the plant, and all treatment plants have a maximum flow rate capacity. Thus, if a centralized treatment plant receives more wastewater on a particular day than what the plant was designed to handle, problems are encountered. For instance, when a treatment plant receives larger-than-normal amounts of untreated raw wastewater, a portion of the untreated wastewater must be diverted into a body of water, such as a river, in order not to exceed the amount of wastewater the plant was designed to handle. As discussed above, discharge of this untreated wastewater into bodies of water will eventually endanger and kill resident plant and aquatic life in the water. Untreated wastewater also contains a number of disease pathogens that are extremely harmful to humans. For instance, untreated wastewater is one of the leading causes of dysentery, which can be life threatening if not properly treated. Thus, if a significant amount of untreated wastewater is discharged into a body of water, that body of water will become unavailable for human consumption. On the other hand, if the treatment plant processes the larger-than-normal amounts of untreated wastewater, instead of diverting a portion into a body of water, the influx of untreated wastewater would wash away the bacteria populations used by the plant to treat the untreated wastewater, which would disrupt the entire biological treatment process of the plant.
Larger-than-normal amounts of untreated wastewater commonly occur because of growth in commercial and residential developments beyond what the centralized wastewater treatment plants were designed to accommodate and because of large amounts of rainfall in a short period of time. Moreover, sewage lines connecting residences and businesses to centralized wastewater treatment plants often develop breaks and cracks which allow rainwater and ground water to seep into the sewage lines. This phenomenon, known as sewage line infiltration, also causes larger-than-normal amounts of wastewater to flow into the centralized treatment plants. Wastewater treatment plants require tremendous community resources in order to accommodate the demands and challenges generated by community growth and development. Often, these resources are not immediately available, and the existing treatment plants are not able to properly treat the increased flow rate of untreated wastewater.
In more rural areas, construction of centralized wastewater treatment plants may be too expensive to build and maintain. In addition, the cost of connecting residences and businesses in rural areas to a centralized treatment plant via sewage lines may be impracticable due to the greater distance between the those residences and businesses. In such areas septic systems are usually utilized to treat wastewater. A septic tank is typically a large tank located underground on an owner's property. Septic tanks are categorized as continuous flow systems because wastewater flows into the septic tank at one end, and the same amount of wastewater that entered will exit the tank at the other end. The purpose of a septic tank is to retain any solids in the wastewater and to allow the liquid wastewater to pass through to prevent field lines leading from the septic tank to a drain field from becoming clogged. However, since the wastewater leaving the septic tank has not been treated, the wastewater will be a detriment to the environment, as discussed above. Furthermore, as solids build up inside the septic tank, a phenomenon known as periodic upset may occur, causing solids to flow out of the septic tank and into the field lines connected to the tank. Eventually, these field lines will clog due to the buildup and carryover of solids. When this occurs, the field lines have to be excavated and cleaned, which means destruction to a portion of the owner's property as well as increased expense to the owner.
Because wastewater leaving a septic tank has not been treated, drain fields covering a certain minimum area of soil are required to filter the wastewater. That minimum area is influenced by factors including the amount of wastewater produced by the household and the soil percolation rate. Different kinds of soil have different percolation rates, and a larger or smaller drain field will be required depending on the characteristics of the soil. Because the percolation rate of soil determines the minimum lot size in a subdivision using septic tanks, the requirement for larger minimum lots where percolation is relatively poor reduces the maximum number of lots available in that subdivision, and the resulting increase in the cost of those lots is passed on to the home buyers.
In view of the problems encountered with using septic tanks to handle wastewater, on-site alternative wastewater treatment systems have been proposed in attempt to cure the deficiencies of septic tanks. A number of the commercially available on-site wastewater treatment systems utilize the continuous flow system discussed above with regard to septic tanks. In a continuous flow system, no wastewater leaves the system unless wastewater enters the system, and unlike at a centralized wastewater treatment plant, there is no operator available at these on-site treatment systems to determine and adjust to changes in flow rate of wastewater entering the systems. Therefore, if a residence or business does not generate any new wastewater for a period of time, such as for several hours or a couple of weeks, the wastewater in these on-site treatment systems remains in the systems because no new wastewater is available to push any wastewater out of the systems.
To treat wastewater, these on-site treatment systems either continuously aerate, or aerate at set periodic times such as every four, eight, or twelve hours, the wastewater. However, in continuous flow systems, there is nothing available to separate the untreated wastewater from the treated wastewater or to distinguish wastewater that has not been treated from wastewater that has been treated, once the two are mixed. Consequently, untreated wastewater is often discharged from continuous flow systems because of this lack of control over what actually gets pushed out of the systems.
Other on-site alternative wastewater treatment systems utilize a pump configuration to transfer wastewater throughout the systems. Although these systems may control when wastewater is discharged from the systems, the systems do not control what is actually getting discharged from the systems because, like the continuous flow systems, there is nothing available in the pump systems to separate the untreated wastewater from the treated wastewater or to distinguish wastewater that has not been treated from wastewater that has been treated, once the two are mixed. As a result, untreated wastewater is often discharged from the pump systems. Moreover, pump systems are expensive to maintain because certain objects commonly found in wastewater often clog the pumps and valves required to control the flow of wastewater through the system, causing frequent maintenance and replacement.
Further, many of the on-site alternative wastewater treatment systems require the property owners to perform daily or periodic adjustments to the systems. Such maintenance is expensive and also cumbersome to the property owner, who is typically inexperienced with regard to wastewater treatment. Often, property owners are not able to determine what the problem is with the system because of the sophistication of the wastewater treatment process. This sophistication also causes property owners not to want to get involved with any daily or periodic adjustments to the system.
Accordingly, an on-site wastewater treatment system capable of separating treated wastewater from untreated wastewater so that treated wastewater is discharged from the system while untreated wastewater is retained in the system is needed. Moreover, an on-site wastewater treatment system having a cost efficient and reliable means of discharging treated wastewater from the system is also needed.